KR101236501B1 - Switching mode power supply and the driving method thereof - Google Patents

Abstract

The present invention relates to a switched mode power supply.

A switching mode power supply according to one aspect of the invention includes a switching transistor coupled to a primary coil of a transformer that rectifies the input alternating voltage to generate an input direct voltage and converts the input direct voltage. The switching mode power supply includes a power supply for supplying power to the secondary side of the transformer according to the operation of the switching transistor, a sense signal corresponding to a feedback voltage corresponding to the voltage on the secondary side of the transformer and a current flowing through the switching transistor and the switching transistor. And a switching controller configured to receive a first signal corresponding to a voltage difference between the first electrode and the second electrode to control on / off of the switching transistor. The switching controller detects and counts the number of times that the voltage level of the first signal and the reference voltage are the same after turning off the switching transistor, and turns on the switching transistor after a point in time at which the counted first number and the variable reference number are the same.

Quasi-Resonant Converters, Frequency, Switches

Description

Switching mode power supply and its driving method {SWITCHING MODE POWER SUPPLY AND THE DRIVING METHOD THEREOF}

1 is a view showing the overall configuration of an SMPS according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a signal generated in each configuration of FIG. 1.

3 is a diagram illustrating a configuration of a PWM signal generator.

4 is a diagram illustrating a switching voltage detector according to a second exemplary embodiment of the present invention.

5 is a diagram illustrating a signal generated according to a second embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching mode power supply (hereinafter referred to as SMPS), and more particularly to an SMPS of a quasi-resonant switching method and a driving method thereof.

SMPS is a device that rectifies the input AC voltage into an input DC voltage (dc-link voltage), and converts the input DC voltage into a DC output voltage having a different level. In this case, the DC output voltage has a magnitude greater or smaller than the input DC voltage. Such SMPS is mainly used for power electronic devices, especially battery power supplies such as mobile phones, laptop computers and the like.

On the other hand, the SMPS of the quasi-resonant switching method includes a quasi-resonant converter. Since the quasi-resonant converter is turned on when the drain voltage value of the transistor serving as the main switch is minimum, the switching loss is reduced. In the quasi-resonant converter, the electromagnetic interference (EMI) spectrum of the quasi-resonant converter is dispersed due to a change in switching frequency caused by the ripple of the input DC voltage. However, as the input AC voltage value increases, the dc-link voltage ripple decreases. As the dc-link voltage ripple decreases, the modulation range of the switching frequency decreases and EMI increases.

In general, EMI creates noise in other devices that use the same power supply. There are various EMI regulations to prevent EMI. As an example of various EMI regulations, there are regulations in which an average value of EMI at a constant bandwidth is set as an upper limit around each frequency and a regulation that an average value of EMI is set as an upper limit. In general, SMPS requires adding a filter or adding an external device to satisfy this regulation. Therefore, it increases the production cost.

SUMMARY OF THE INVENTION The present invention provides an SMPS and a driving method thereof to reduce EMI by changing a switching frequency of a switching transistor regardless of an input AC voltage.

According to one aspect of the present invention, a switching mode power supply includes a switching transistor which rectifies an input AC voltage to generate an input DC voltage, and is coupled to a primary coil of a transformer for converting the input DC voltage, wherein the switching A power supply unit supplying power to the secondary side of the transformer according to an operation of the transistor, a sense signal corresponding to a feedback voltage corresponding to a voltage on the secondary side of the transformer and a current flowing through the switching transistor, and a first of the switching transistor And a switching controller configured to receive a first signal corresponding to a voltage difference between an electrode and a second electrode to control on / off of the switching transistor, wherein the switching controller is configured to, after turning off the switching transistor, the first signal. Detects the number of times the signal's voltage level and reference voltage are equal, Agent, and after the counted number of times with the same time varying the reference frequency, and determines the turn-on time of the switching transistor. At this time, when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage, the switching transistor is turned on.

In this case, the variable reference number includes at least a first reference number or a second reference number having different values, and the switching controller counts the number of turn-on times of the switching transistor, and determines the variable reference number according to a count result. Change it.

The switching mode power supply further includes a switching voltage detector configured to generate a first signal corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor, wherein the switching controller comprises: a voltage and a reference of the first signal; By comparing the voltages, if the reference voltage and the voltage of the first signal are the same as the first reference number, after the delay time, the operation of turning on the switching transistor is performed at least once, and then the voltage of the first signal. And comparing the reference voltage with each other, if the reference voltage is equal to the voltage of the first signal by the second reference number of times, turning on the switching transistor after the delay time.

Alternatively, the switching control unit changes the reference number of times when a predetermined time elapses. The switching control unit and the switching transistor are formed in one pack, or the switching control unit and the switching transistor are each formed in a separate pack.

According to another aspect of the present invention, a switching mode power supply includes a switching transistor configured to rectify an input AC voltage to generate an input DC voltage, and to be coupled to a primary coil of a transformer that converts the input DC voltage. A power supply unit supplying power to the secondary side of the transformer according to an operation of the transistor, a sense signal corresponding to a feedback voltage corresponding to a voltage on the secondary side of the transformer and a current flowing through the switching transistor, and a first of the switching transistor And a switching controller configured to receive a first signal corresponding to a voltage difference between an electrode and a second electrode and a first signal generated by a reference voltage to control on / off of the switching transistor. After turning off the switching transistor, the first signal has a first level. And a turn-on time point of the switching transistor is determined after a point in time at which the counted number and the variable reference number are the same. At this time, when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage, the switching transistor is turned on.

In this case, the variable reference number includes a first reference number or a second reference number having at least a different value, and the switching controller counts the number of turn-on times of the switching transistor, and according to the count result, the variable reference number Change

The switching mode power supply compares the first current generated by the first voltage and the reference voltage difference with a reference current, so that the first level of the first level is increased during a period in which the first current has a higher value than the reference current. The apparatus further includes a switching voltage detector configured to generate one signal. The switching controller is further configured to count a section in which the first signal has the first level, count the first reference number of times, and then, after a delay time from the time when the first signal first changes to the first level, After performing an operation of turning on a switching transistor at least once, after counting the interval in which the first signal has the first level, and counting the second reference number of times, the first signal is first the first level. After the delay time from the time point to change, to turn on the switching transistor.

Or, when the predetermined time passes, the reference number of times is changed. The switching control unit and the switching transistor are formed in one pack, or the switching control unit and the switching transistor are each formed in a separate pack.

According to still another aspect of the present invention, there is provided a method of driving a switched mode power supply, the method comprising: rectifying an input AC voltage to generate an input DC voltage, and converting the input DC voltage according to on / off of a switching transistor to generate an output DC voltage. In the driving method of the switching mode power supply,

a) generating a feedback signal corresponding to the output DC voltage and a sensing signal corresponding to a current flowing through the switching transistor and a first signal corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor,

b) detecting and counting a first number of times that the voltage level of the first signal is equal to the reference voltage after the switching transistor is turned off;

c) determining a turn-on time of the switching transistor after a time point at which the counted first number and the variable reference number are the same; and

and d) changing the variable reference number of times after repeating step c) by a predetermined number of modulation references.

According to still another aspect of the present invention, there is provided a method of driving a switched mode power supply, the method comprising: rectifying an input AC voltage to generate an input DC voltage, and converting the input DC voltage according to on / off of a switching transistor to generate an output DC voltage. In the driving method of the switching mode power supply,

a) generated by a feedback voltage corresponding to the output DC voltage and a sensing signal corresponding to a current flowing through the switching transistor and a first voltage and a reference voltage corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor Generating a first signal to perform,

b) after turning off the switching transistor, detecting and counting a first number of times the first signal has a first level;

c) determining to turn on the switching transistor after a point in time at which the counted first number is equal to the variable reference number, and

and d) changing the variable reference number of times after repeating step c) by a predetermined number of modulation references.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

Hereinafter, a quasi-resonant converter and an SMPS using the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the overall configuration of an SMPS according to an embodiment of the present invention.

As shown in FIG. 1, an SMPS according to an exemplary embodiment of the present invention includes a power supply unit 100, an output unit 200, a bias voltage supply unit 300, a switching controller 400, and a switch voltage detector 500. do.

The power supply unit 100 includes a bridge diode BD for rectifying the AC input AC, a capacitor Cin for smoothing the rectified voltage, and a primary coil L1 of a transformer having one end connected to the capacitor Cin. It includes. The power supply unit 100 converts the AC voltage AC to the DC voltage Vin by the bridge diode BD and the capacitor Cin, and according to the duty of the switching transistor Qsw, the secondary side of the transformer That is, power is supplied to the output unit 200. In addition, the power supply unit 100 includes a modulation determination unit 110 that determines whether to perform an operation for switching frequency modulation in the switching controller 400 according to the level of the input AC voltage. If the DC voltage Vin generated by rectifying the input AC voltage has a value equal to or less than the modulation reference voltage, the modulation determination unit 110 generates sufficient ripple, and thus, no separate frequency modulation is required in the switching controller 400. I do not think. Then, the frequency modulation control signal FMS for stopping the frequency modulation to the switching controller 400 is transmitted to the input terminal in5 of the switching controller 400. On the contrary, when the DC voltage Vin exceeds the modulation reference voltage, the frequency modulation control signal FMS is transmitted to the input terminal in5 of the switching controller 400 for switching frequency modulation to prevent EMI. . According to an embodiment of the present invention, when the frequency modulation of the switching transistor occurs due to the ripple of the input AC voltage, and according to the EMI regulation by the generated frequency modulation, the highest input AC voltage among the input AC voltages is input. It can be set to the DC voltage Vin corresponding to.

The output unit 200 is a diode (D1) having an anode connected to the secondary coil (L2) of the transformer, the secondary coil (L2) of the transformer, a capacitor connected between the cathode of the diode (D1) and ground (C1). The voltage across the capacitor C1 is the output voltage Vo.

The bias voltage supply unit 300 is connected between a diode D2 having an anode connected to one end of the secondary coil L3 of the transformer and a secondary coil L3 of the transformer, and a cathode of the diode D2 and a ground. Capacitor C2 is included. The switching controller 400 may be generally implemented through an IC, and the bias voltage supply unit 300 supplies a bias voltage Vcc for operating the IC. That is, when the switching transistor Qsw starts switching, the secondary coil L3 and the diode D2 of the transformer operate to charge the bias voltage Vcc across the capacitor C2.

The switch voltage detector 500 generates a sink signal VS corresponding to the drain-source voltage of the switching transistor Qsw by using the voltage signal VL of the secondary coil L3 of the transformer to switch the switching controller 400. To be sent). The switch voltage detector 500 includes resistors R1 and R2 and a capacitor C3. A resistor (R1) and a resistor (R2) are connected in series between the transformer secondary coil (L3) and ground, and a capacitor (C3) in parallel between the contact of the resistor (R1) and resistor (R2) and ground. Connected. The secondary coil L3 of the transformer reflects the voltage across the primary coil L1, and the voltage across the primary coil L1 equals the drain-source voltage Vds of the switching transistor Qsw by the Vin voltage. Minus voltage. Accordingly, the voltage VL across the secondary coil L3 of the transformer reflects the drain-source voltage of the switching transistor Qsw. Here, the resistors R1 and R2 and the capacitor C3 serve as RC filters (that is, as a delay circuit), and the voltage of the sink signal VS corresponds to the drain source voltage Vds of the switching transistor Qsw. .

The switching controller 400 includes a pulse with modulator (PWM) signal generator 410, a zero crossing detection unit 420, a counter 430, and an oscillator 440. The switching controller 400 receives a feedback signal Vfb, a signal (hereinafter, referred to as a 'sensing signal') (Vsense) that senses a current Ids flowing through the switching transistor Qsw, and a sink signal VS. The gate control signal VGS for controlling the on / off of the switching transistor Qsw is output. Here, the feedback signal Vfb is a signal having information corresponding to the output voltage Vo and is used to determine the turn-off time of the switching transistor Qsw. A method of generating the feedback signal Vfb may use a photocoupled photodiode and a transistor, and a detailed description thereof will be omitted since a person skilled in the art can easily understand the present invention.

The PWM signal generator 410 receives a clock signal CLK, a sensing signal Vsense, and a feedback signal Vfb transmitted from the oscillator 430 to control the turn-on / turn-off of the switching transistor Qsw. Outputs (VGS) A detailed description will be described later with reference to FIG. 3.

The zero crossing detection unit 420 receives the sync signal VS of the bias voltage supply unit 300, detects a point having the same value as the second reference voltage Vref2, and counts the detected point. As a result of the counting, when the same point as the sync signal VS and the second reference voltage Vref2 is counted by the reference number CR, the detection signal DS is output to the oscillator 440 after being delayed by the delay time Td. do. The reference number CR according to the embodiment of the present invention is controlled by the counter 430. In addition, in the zero crossing detection unit 420 according to an exemplary embodiment of the present invention, the delay time Td may be set by a user, and a time point at which the waveform of the sync signal VS crosses the second reference voltage Vref2. And it may be set in consideration of the lowest (valley). In detail, the present invention is to compensate for a difference between a point at which the sync signal VS and the second reference voltage Vref2 intersect and a valley of the resonance waveform. The delay time Td may be preset according to the resonant waveform period of the drain-source voltage of the switching transistor. The delay time Td may be set at a time interval smaller than a period corresponding to one quarter of the shortest resonant waveform period. Can be set. The zero crossing detector 420 determines a reference number according to the frequency modulation control signal FMS transmitted from the modulation determiner 110. When the frequency modulation control signal FMS indicates frequency modulation, the delay time Td after counting the point at which the sync signal VS crosses the second reference voltage Vref2 by the reference number set by the counter 430. After delaying by), the detection signal AS is transmitted to the oscillator 440. If the frequency modulation control signal FMS does not indicate frequency modulation, after counting the points where the sync signal VS crosses the second reference voltage Vref2 by a predetermined reference number, and after delaying the delay time Td, The detection signal DS is transmitted to the oscillator 440. At this time, the set reference number is not determined by the counter 430, but may be a value predetermined by the user as a predetermined value.

When the oscillator 440 detects the detection signal DS, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits the generated clock signal CLK to the PWM signal generator 410.

The counter 430 determines whether to change the reference number of times according to the frequency modulation control signal FMS. The counter 430 counts the number of times the clock signal CLK output from the oscillator 440 turns on the switching transistor, and sets the reference number according to the count result. The switching controller 400 according to the exemplary embodiment of the present invention changes the reference number of the zero crossing detector 420 for frequency modulation of the switching transistor Qsw. In this case, the reference number may be changed at every time of turning on the switching transistor Qsw, and the reference number may be changed every time the clock signal CLK is counted by a predetermined number of times. Irregularly, a random variable may be generated, and the reference number may be changed when the random variable is compared with the number of times the clock signal CLK is counted. After a predetermined time elapses, the reference number may be changed, and the predetermined time may be determined irregularly.

Meanwhile, the drain of the switching transistor Qsw is connected to the other end of the primary coil L1 of the transformer, and the sensing resistor Rsense is connected between the source and the ground of the switching transistor Qsw. In addition, the resonant capacitor CR may be separately connected between the drain and the source of the switching transistor Qsw, and when the resonant capacitor CR is not used, the parasitic capacitance between the drain and the source of the switching transistor Qsw is used for resonance. do. In the following description, it is assumed that a resonant capacitor CR is used for convenience. In FIG. 1, the switching transistor Qsw is represented as an N-channel MOSFET, but may be replaced by another switching transistor serving as a switch. The switching transistor Qsw according to the embodiment of the present invention has a drain electrode and a source electrode as first and second electrodes, and a gate electrode as a control electrode. The output signal VGS of the PWM signal generator 410 is input to the gate electrode, and the switching transistor Qsw is controlled by the output signal VGS to be turned on / off.

Hereinafter, a driving method of an SMPS according to an embodiment of the present invention will be described with reference to FIG. 2.

FIG. 2 is a diagram illustrating a signal generated in each configuration of FIG. 1.

First, when the output signal VGS of the PWM signal generator 410 becomes high at the time T1, the switching transistor Qsw is turned on. At this time, as shown in FIG. 2A, the current Ids flowing through the switching transistor Qsw increases with a predetermined slope Vin / L1. The current Ids is converted into the sensing signal Vsense by the sensing resistor Rsense and transmitted to the PWM signal generator 410, and the PWM signal generator 410 is the feedback signal Vfb and the sensing signal (S). Vsense) is compared to change the VGS signal from the high state to the low state at time T2. Accordingly, the switching transistor Qsw is turned off at the time T2.

When the switching transistor Qsw is turned off at the time T2, as shown in FIG. 2B, the current Is flowing through the diode D1 decreases to zero with a slope of -Vo / L2. . On the other hand, when the switching transistor Qsw is turned off, the drain-source voltage Vds of the switching transistor Qsw is [Vin + Vo * Np / Ns] (where Np and Ns are the primary and secondary sides of the transformer. To turn ratio).

At a time when the current Is becomes zero, that is, at T3, the diode D1 is turned off and the secondary coil L2 is converted into a high impedance state. Accordingly, resonance occurs between the primary coil L1 of the transformer and the resonance capacitor CR, and the resonance period is determined by the inductance of the primary coil L1 and the capacitance value of the resonance capacitor CR. As described above, when resonance occurs between the primary coil L1 of the transformer and the resonance capacitor CR, the Vds signal is fluctuated by drawing a cosine curve based on the Vin voltage. As shown in FIG. 2C, the voltage signal VL corresponding to the drain-source voltage Vds of the switching transistor Qsw also has a cosine curve based on the first reference voltage Vref1. And it fluctuates. The voltage signal VL is determined according to the voltage generated in the secondary coil L3, and this voltage reflects the drain-source voltage Vds signal of the switching transistor Qsw as it is.

On the other hand, the switch voltage detector 500 generates the sync signal VS as shown in FIG. That is, the sink signal VS as shown in FIG. 2D is generated by the resistors R1 and R2 and the capacitor C5 of the switch voltage detector 500. The sync signal VS rises or falls slightly later than the voltage signal VL due to the RC time constant. As a result, the point where the Vds signal is minimum and the point where the sync signal VS is minimum are slightly shifted. That is, the resistors R1 and R2 and the capacitor C5 of the switch voltage detector 500 serve as a delay circuit for delaying the voltage signal VL to generate the sink signal VS.

As illustrated in FIG. 2E, the zero crossing detection unit 420 detects a time point at which the sync signal VS crosses the second reference voltage Vref2, and a time point C1, C2, C3, C4, and C5. Then, the zero crossing detection unit 420 counts the number of crossings and compares it with the reference number. In FIG. 2, the case where the reference number is five times will be described first. However, the present invention is not limited thereto. The zero crossing detection unit 420 may generate and count the high level pulse HP at each time point of crossing. After the fifth high level pulse HP is generated, the zero crossing detection unit 420 may delay the delay time Td to generate a high level pulse HP. The detection signal AS having the pulse is generated and transmitted to the oscillator 440.

Then, as shown in (f) of FIG. 2, at time point T4, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits it to the PWM signal generator 410.

As shown in FIG. 2G, the PWM signal generator 410 changes the VGS signal to a high level at the polling timing T5 of the clock signal CLK. Accordingly, the switching transistor Qsw is turned on at the lowest point T5 after the sync signal VS crosses the second reference voltage Vref2 five times.

The reference count of the zero crossing detection unit 420 according to the embodiment of the present invention is set to 5, but is not limited thereto. In this manner, while controlling the on / off of the switching transistor Qsw by the modulation reference number k, the counter 430 has a high level pulse with the clock signal CLK output from the oscillator 440. The number of times is counted to determine whether the on / off of the switching transistor Qsw is controlled by the set modulation reference number k. When the counter 430 counts the clock signal CLK having the high level pulse by the set modulation reference number k, the counter 430 changes the reference number to three. At this time, as mentioned above, the modulation reference number k may change at regular intervals, or may change irregularly after a predetermined time.

The operation when the reference number is changed to three will be described below. After being turned on at the time point T6, it is turned off at the time point T7, and then the voltage signal VL is resonated as described above.

As illustrated in (e) of FIG. 2, the zero crossing detector 420 detects a time point at which the sync signal VS crosses the second reference voltage Vref2, and a time point C6, C7, and C8. Then, the zero crossing detection unit 420 counts the number of crossings and compares it with the reference number. Since the reference count is three times, the zero crossing detection unit 420 generates and counts a high level pulse at each time point of crossing, and after generating the third high level pulse, delays the high level pulse after a delay time Td. The detection signal AS is generated and transmitted to the oscillator 440.

Then, as shown in (f) of FIG. 2, at time point T8, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits it to the PWM signal generator 410.

As shown in FIG. 2G, the PWM signal generator 410 changes the VGS signal to a high level at the polling timing T9 of the clock signal CLK. Accordingly, the switching transistor Qsw is turned on at the lowest point T9 after the sink signal VS crosses the second reference voltage Vref three times.

In this manner, while controlling the on / off of the switching transistor Qsw by the set number k, the counter 430 counts the number of times that the clock signal CLK output from the oscillator 440 has a high level pulse. It is determined whether the on / off of the switching transistor Qsw has been controlled by counting the number of times k. When the counter 430 counts the clock signal CLK having the high level pulse by the set number k, the counter 430 changes the reference number to a value other than three.

Hereinafter, the PWM signal generator 410 will be described with reference to FIG. 3.

3 is a diagram illustrating a configuration of the PWM signal generator 410. As shown in FIG. 3, the PWM signal generator 410 includes a PWM comparator 411, a PWM flip-flop 412, a NOR gate 413, and a gate driver 414.

The PWM comparator 411 compares the feedback signal with the sensing signal, and outputs a high level signal to the reset stage R of the PWM flip-flop 412 when the sensing signal has a higher level than the feedback signal.

When the high level signal is input to the reset terminal of the PWM flip-flop 412, the high level signal is output to the NOR gate 413 at the inverting output terminal / Q of the PWM flip-flop 412. Then, regardless of the level of the clock signal CLK of the oscillator 440, the NOR gate 413 outputs a low level signal, and at this time, the gate driver 414 turns off the switching transistor Qsw.

Thereafter, as shown in FIG. 2D, when the clock signal CLK becomes a high level pulse, the clock signal CLK is input to the set terminal S of the PWM flip-flop 412 to invert the PWM flip-flop 412. A low level signal is output to the output terminal / Q and input to the NOR gate 413. As in the time points T1, T5, T6, and T9, the NOR gate 413 outputs a high level signal to the gate driver 414 at the polling timing of the clock signal because the input signals are all at the low level.

The gate driver then turns on the switching transistor Qsw at points T1, T5, T6, and T9.

As described above, in the switching mode power supply and the driving method thereof, the number of times that the sink signal VS corresponding to the drain-source voltage Vds of the switching transistor Qsw becomes the second reference voltage is counted. The on / off of the switching transistor Qsw is controlled while changing the reference number at an arbitrary interval (modulation reference number). Thus, the frequency modulation range of the switching transistor Qsw is maintained regardless of the level of the input AC voltage. As a result, the input AC voltage increases, thereby reducing the frequency modulation range of the switching transistor Qsw due to the decrease in the ripple width of the dc-link voltage. Therefore, EMI can be reduced.

Hereinafter, an SMPS for performing frequency modulation of a switching transistor by current sensing according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5.

4 illustrates a switching voltage detector 500 ′ according to a second embodiment of the present invention.

As shown in FIG. 4, the switching voltage detector 500 ′ according to the second embodiment of the present invention detects the drain-source voltage of the switching transistor Qsw by using a current-mirror method. do.

The switching voltage detector 500 'includes a reference current source Ir, a power supply Vcc, a resistor R4, a resistor R5, a first BJT (B1), a diode-connected second BJT (B2), and a detection transistor ( M) and comparator 510. The detection transistor M according to the second embodiment of the present invention is an N-channel MOSFET and has a drain electrode, a source electrode, and a gate electrode as the first electrode, the second electrode, and the control electrode. A resistor R3 is connected between the switching voltage detector 500 'and the secondary coil L3 to adjust the current signal i generated according to the voltage difference between the voltage VC and the voltage signal VL. .

The reference voltage Vr is input to the non-inverting terminal + of the comparator 510, and the voltage VC is input to the negative terminal (−). If the voltage VC is greater than the reference voltage Vr, the transistor is turned off. If the voltage VC is less than the reference voltage Vr, the transistor is turned on and the voltage VC rises. Therefore, the voltage VC is maintained at the same value as the reference voltage Vr.

When the voltage signal VL is smaller than the voltage VC, a current i generated according to the voltage value of the voltage signal VL and the voltage difference of the voltage VC flows in the diode-connected second BJT, and the current-mirror The current i flows through the emitter terminal of the first BJT B1. At this time, when the current i is smaller than the reference current source Ir, a low level sink signal VS 'is output. When the current i is larger than the reference current source Ir, the high level sink signal VS' is output. ) Is output. When the current i generated according to the embodiment of the present invention has a larger value than the reference current source Ir, and outputs the high level sync signal VS ', the value of the voltage signal VS is sensed based on the sensing reference. Set to voltage Vref3. Therefore, in the period where the voltage signal VS is less than or equal to the sensing reference voltage Vref3, the sink signal VS ′ becomes a high level.

The zero crossing detection unit 420 'counts a section in which the high level sync signal VS' is output and compares it with the reference number of times. When the zero crossing detection unit 420 'is equal to the reference number of times as a result of the comparison, the detection signal is delayed by the delay time Td' from the moment when the rising timing at which the sink signal VS 'changes to a high level is detected thereafter. AS 'to the oscillator 440.

When the oscillator 440 receives the detection signal AS ′, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits the generated clock signal CLK to the PWM signal generator 410.

5 illustrates a signal generated in an SMPS according to a second embodiment of the present invention.

When the output signal VGS of the PWM signal generator 410 becomes high at time T11, the switching transistor Qsw is turned on. At this time, as shown in FIG. 5A, the current Ids flowing through the switching transistor Qsw increases with a predetermined slope Vin / L1. The current Ids is converted into the sensing signal Vsense by the sensing resistor Rsense and transmitted to the PWM signal generator 410, and the PWM signal generator 410 is the feedback signal Vfb and the sensing signal (S). Vsense) is compared to change the VGS signal from the high state to the low state at time T12. Accordingly, the switching transistor Qsw is turned off at the time T2.

When the switching transistor Qsw is turned off at the time T12, as shown in FIG. 5B, the current Is flowing through the diode D1 decreases to zero with a slope of -Vo / L2. .

At the time T13 when the current Is becomes zero, resonance occurs between the primary coil L1 of the transformer and the resonant capacitor CR, and the resonant period is the inductance of the primary coil L1 and the resonant capacitor ( It is determined by the capacitance value of CR). As described above, when resonance occurs between the primary coil L1 of the transformer and the resonance capacitor CR, the Vds signal is fluctuated by drawing a cosine curve based on the Vin voltage. As shown in FIG. 5C, the voltage signal VL corresponding to the drain-source voltage Vds of the switching transistor Qsw also has a cosine curve based on the first reference voltage Vref1. And it fluctuates. The voltage signal VL is determined according to the voltage generated in the secondary coil L3, and this voltage reflects the drain-source voltage Vds signal of the switching transistor Qsw as it is.

On the other hand, the switch voltage detector 500 generates the high level sync signal VS 'during the period T14 and the period T15 in FIG. 5C. If the reference count according to the second embodiment of the present invention is assumed to be 2, the zero crossing detection unit 420 detects the high-level sync signal VS 'by the reference number of times, and then the first sync signal VS'. The detection signal AS 'is generated after the delay time Td' from the time T16 at which the rising time occurs, and the detection signal AS 'is transmitted to the oscillator 440. Then, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits the clock signal CLK to the PWM signal generator 410 at a time point T17. In FIG. 5, the case where the reference number is twice is described first. However, the present invention is not limited thereto.

As shown in FIG. 5E, the PWM signal generator 410 changes the VGS signal to a high level at the polling timing T18 of the clock signal CLK. Accordingly, the switching transistor Qsw is turned on at T18, when the voltage signal VL is at the lowest point, after sensing the section in which the sink signal VS 'is high level twice.

Although the reference number of the zero crossing detection unit 420 according to the second embodiment of the present invention is set to twice, the present invention is not limited thereto. In this manner, while controlling the on / off of the switching transistor Qsw by the modulation reference number k ', the counter 430 outputs a high level pulse by the clock signal CLK output from the oscillator 440. It is determined whether the on / off of the switching transistor Qsw is controlled by the set modulation reference number k 'by counting the number of times. When the counter 430 counts the clock signal CLK having the high level pulse by the set modulation reference number k ', the counter 430 changes the reference number once. At this time, as mentioned above, the modulation reference number k may change at regular intervals, or may change irregularly after a predetermined time.

The operation when the reference count is changed once is described below. After being turned on at the time point T21, it is turned off at the time point T22, and then the voltage signal VL is resonated as described above.

The zero crossing detection unit 420 detects the signal AS 'after the delay time Td' from the time point T24 when the sink signal VS 'has a high level in the period T23 and the first sink signal VS' rising time occurs. ) Is delivered to the oscillator 440. Then, the oscillator 440 generates a clock signal CLK having a high level pulse and transmits the clock signal CLK to the PWM signal generator 410 at a time point T25.

As shown in FIG. 5E, the PWM signal generator 410 changes the VGS signal to a high level at the polling timing T26 of the clock signal CLK. Accordingly, the switching transistor Qsw is turned on at a time point T26 at which the voltage signal VL is the lowest after detecting a section in which the sink signal VS 'is at a high level once.

In this manner, while controlling the on / off of the switching transistor Qsw by the modulation reference number k ', the counter 430 outputs a high level pulse by the clock signal CLK output from the oscillator 440. It is determined whether the on / off of the switching transistor Qsw is controlled by the number of modulation reference times k 'by counting the number of times of the number of times. When the counter 430 counts the clock signal CLK having the pulse having the high level by the modulation reference number k ', the counter 430 changes the reference number to a value other than once.

As described above, in the switching mode power supply and the driving method thereof, the voltage signal VL corresponding to the drain-source voltage Vds of the switching transistor Qsw is smaller than the third reference voltage. The on / off of the switching transistor Qsw is controlled while changing the reference number at an arbitrary interval (modulation reference number). Thus, the frequency modulation range of the switching transistor Qsw is maintained regardless of the level of the input AC voltage. As a result, the input AC voltage increases, thereby reducing the frequency modulation range of the switching transistor Qsw due to the decrease in the ripple width of the dc-link voltage. Therefore, EMI can be reduced.

The first and second embodiments of the present invention described so far can be applied to both a SMPS in which the switching transistor and the switching control unit are formed in one pack, and SMPS in which the switching transistor and the switching control unit are divided and formed in different packs.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

As described above, according to an aspect of the present invention, there is provided a switching mode power supply and a driving method thereof capable of sensing a voltage or current signal to internally adjust a switching frequency modulation range without an external device.

Accordingly, the present invention provides a switching mode power supply and its driving method capable of reducing EMI by maintaining a constant switching frequency modulation range regardless of an input voltage.

Claims (46)

And a switching transistor coupled to the primary coil of the transformer for rectifying the input AC voltage to generate an input DC voltage, and converting the input DC voltage, wherein power is supplied to the secondary side of the transformer according to the operation of the switching transistor. A power supply unit for supplying, and Receiving a feedback voltage corresponding to a voltage on a secondary side of the transformer and a sensing signal corresponding to a current flowing through the switching transistor and a first signal corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor, A switching controller for controlling on / off of the switching transistor, Wherein the switching control unit comprises: After turning off the switching transistor, detecting and counting the number of times that the voltage level of the first signal and the reference voltage are equal to each other; , The variable reference number of times includes at least a first reference number or a second reference number each having a different value. delete The method of claim 1, Wherein the switching control unit comprises: And switching the variable reference number according to a count result by counting the number of turn-on times of the switching transistor. The method of claim 1, Wherein the switching control unit comprises: A switching mode power supply for changing the reference number of times after a predetermined time has elapsed. The method of claim 1, A switching voltage detector for generating a first signal corresponding to the voltage difference between the first electrode and the second electrode of the switching transistor. Switching mode power supply further comprising. The method of claim 5, Wherein the switching control unit comprises: After comparing the voltage of the first signal and the reference voltage, if the reference voltage is equal to the voltage of the first signal by the first reference number of times, after the delay time, the operation to turn on the switching transistor at least once , A switching mode power for comparing the voltage of the first signal with a reference voltage and turning on the switching transistor after the delay time when the reference voltage is equal to the voltage of the first signal by the second reference number of times; Supply. The method of claim 6, And switching on the switching transistor when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage. The method of claim 7, wherein Wherein the switching control unit comprises: A zero crossing detector configured to count the number of times the first signal intersects the reference voltage, and generate a detection signal after the delay time if the number of times that the first signal crosses the reference voltage is equal to the variable reference number of times; An oscillator for generating a clock signal having a pulse of a second level when the detection signal is input, and A counter for counting the number of times the clock signal becomes a pulse of a second level and changing the variable reference number of times according to the count result Switching mode power supply comprising a. 9. The method of claim 8, The first signal has a phase delayed from the phase of the voltage difference between the first electrode and the second electrode of the switching transistor, The delay time is, And a switching mode power supply for compensating for a difference between a time point at which the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage and a time point at which the first signal and the reference voltage are the same. 9. The method of claim 8, The counter, The switching mode power supply for changing the variable reference number, if the count result, the comparison is equal to the number of modulation reference. The method of claim 10, And the number of modulation references varies for switching frequency modulation of the switching transistor. The method of claim 1, Wherein the switching control unit comprises: And when the input DC voltage is less than or equal to a modulation reference voltage, when the voltage difference between the first electrode and the second electrode of the switching transistor is the first lowest voltage, the switching mode power supply. The method of claim 12, The modulation reference voltage is, The switching mode power supply being the largest input DC voltage when the frequency modulation of the switching transistor occurs due to the ripple of the input DC voltage, and EMI is regulated by the frequency modulation. The method according to any one of claims 1 and 3 to 13 And the switching controller and the switching transistor are formed in one pack. The method according to any one of claims 1 and 3 to 13 And the switching control unit and the switching transistor are each formed in a separate pack. And a switching transistor coupled to the primary coil of the transformer for rectifying the input AC voltage to generate an input DC voltage, and converting the input DC voltage, wherein power is supplied to the secondary side of the transformer according to the operation of the switching transistor. A power supply unit for supplying, and A feedback voltage corresponding to the voltage on the secondary side of the transformer and a sense signal corresponding to the current flowing through the switching transistor, and a first voltage and a reference voltage corresponding to the voltage difference between the first electrode and the second electrode of the switching transistor. A switching controller configured to receive a generated first signal and control on / off of the switching transistor, Wherein the switching control unit comprises: After the turn-off of the switching transistor, the interval in which the first signal has a first level is counted, and after the point in time at which the counted count is equal to the variable reference number in time, the turn-on time of the switching transistor is determined, The variable reference number of times includes at least a first reference number or a second reference number each having a different value. delete 17. The method of claim 16, Wherein the switching control unit comprises: And switching the variable reference number according to a count result by counting the number of turn-on times of the switching transistor. 17. The method of claim 16, Wherein the switching control unit comprises: A switching mode power supply for changing the reference number of times after a predetermined time has elapsed. 19. The method of claim 18, A switching voltage that generates the first signal of the first level during a period in which the first current has a higher value than the reference current by comparing the first current generated by the first voltage and the reference voltage difference with the reference current. Detector Switching mode power supply further comprising. 21. The method of claim 20, Wherein the switching control unit comprises: After the first signal counts the interval having the first level, the first reference number of times, after the delay time from the time when the first signal first changes to the first level, turning on the switching transistor After performing an action at least once, After the first signal counts the section having the first level and is counted by the second reference number, the switching transistor is turned on after the delay time from the time when the first signal first changes to the first level. Switching mode power supply to perform the operation. 22. The method of claim 21, And switching on the switching transistor when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage. 23. The method of claim 22, Wherein the switching control unit comprises: Generating a detection signal after the delay time from a time when the first signal first changes to the first level after counting a section in which the first signal has the first level and being equal to the variable reference number of times; Zero crossing detector, An oscillator for generating a clock signal having a pulse of a second level when the detection signal is input, and A counter for counting the number of times the clock signal becomes the pulse of the second level, and changing the variable reference number of times according to the count result Switching mode power supply comprising a. 24. The method of claim 23, The delay time is, Switching mode power supply for compensating for the difference between the time when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage and the time when the first signal becomes the first level. 24. The method of claim 23, The counter, The switching mode power supply for changing the variable reference number, if the count result, the comparison is equal to the number of modulation reference. 26. The method of claim 25, And the number of modulation references varies for switching frequency modulation of the switching transistor. 17. The method of claim 16, Wherein the switching control unit comprises: And when the input DC voltage is less than or equal to a modulation reference voltage, when the voltage difference between the first electrode and the second electrode of the switching transistor is the first lowest voltage, the switching mode power supply. 28. The method of claim 27, The modulation reference voltage is, The switching mode power supply being the largest input DC voltage when the frequency modulation of the switching transistor occurs due to the ripple of the input DC voltage, and EMI is regulated by the frequency modulation. 29. The method according to any one of claims 16 and 18 to 28. And the switching controller and the switching transistor are formed in one pack. 29. The method according to any one of claims 16 and 18 to 28. And the switching control unit and the switching transistor are each formed in a separate pack. In the driving method of the switching mode power supply for rectifying the input AC voltage to generate an input DC voltage, and converts the input DC voltage in accordance with the on / off of the switching transistor to generate an output DC voltage, a) generating a feedback signal corresponding to the output DC voltage and a sensing signal corresponding to a current flowing through the switching transistor and a first signal corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor, b) detecting and counting a first number of times that the voltage level of the first signal is equal to the reference voltage after the switching transistor is turned off; c) determining a turn-on time of the switching transistor after a time point at which the counted first number and the variable reference number are the same; and d) changing the variable reference number of times after repeating step c) by a predetermined number of modulation references; Including, And the variable reference number of times includes at least a first reference number or a second reference number having different values. The method of claim 31, wherein Step d), Counting the number of times of performing the step c) and changing the variable reference number from the first reference number to the second reference number if the count result is equal to the modulation reference number. Driving method. delete The method of claim 31, wherein Step d), The method of driving a switched mode power supply for changing the variable reference number of times after a predetermined time elapses. The method of claim 31, 32, or 34, wherein The step c) includes the step of turning on the switching transistor when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage. 35. The method according to any one of claims 31, 32, and 34. And the number of modulation references varies to modulate the switching frequency of the switching transistor. The method of claim 31, 32, or 34, wherein e) driving the switching mode power supply when the input DC voltage is less than the modulation reference voltage, when the voltage difference between the first electrode and the second electrode of the switching transistor is the first lowest voltage; Way. The method of claim 37, The modulation reference voltage is, And a frequency modulation of the switching transistor caused by the ripple of the input DC voltage, and the largest input DC voltage when the EMI is regulated by the frequency modulation. In the driving method of the switching mode power supply for rectifying the input AC voltage to generate an input DC voltage, and converts the input DC voltage in accordance with the on / off of the switching transistor to generate an output DC voltage, a) generated by a feedback voltage corresponding to the output DC voltage and a sensing signal corresponding to a current flowing through the switching transistor and a first voltage and a reference voltage corresponding to a voltage difference between the first electrode and the second electrode of the switching transistor Generating a first signal to perform, b) after turning off the switching transistor, detecting and counting a first number of times the first signal has a first level; c) determining a turn-on time of the switching transistor after a time point at which the counted first number and the variable reference number are the same; and d) changing the variable reference number of times after repeating step c) by a predetermined number of modulation references; Including, And the variable reference number of times includes at least a first reference number or a second reference number having different values. 40. The method of claim 39, Step d), Counting the number of times of performing the step c) and changing the variable reference number from the first reference number to the second reference number if the count result is equal to the modulation reference number. Driving method. delete 40. The method of claim 39, d) step, The method of driving a switched mode power supply for changing the variable reference number of times after a predetermined time elapses. 43. The method of any one of claims 39, 40, and 42, wherein The step c) includes the step of turning on the switching transistor when the voltage difference between the first electrode and the second electrode of the switching transistor has the lowest voltage. 43. The method of any one of claims 39, 40, and 42. And the number of modulation references varies to modulate the switching frequency of the switching transistor. 43. The method of any one of claims 39, 40, and 42, wherein e) driving the switching mode power supply when the input DC voltage is less than the modulation reference voltage, when the voltage difference between the first electrode and the second electrode of the switching transistor is the first lowest voltage; Way. The method of claim 45, The modulation reference voltage is, And a frequency modulation of the switching transistor caused by the ripple of the input DC voltage, and the largest input DC voltage when the EMI is regulated by the frequency modulation.

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